1. Field of the Invention
The present invention relates to a substrate polishing method for planarizing the surface of a substrate such as a semiconductor substrate and a liquid crystal substrate, and a method of manufacturing semiconductor device using the substrate polishing method.
2. Description of the Related Art
In a manufacturing process of semiconductor devices, chemical mechanical polishing (CMP) is widely used for planarizing an interlayer insulating film, forming a damascene interconnect structure, and forming a shallow trench isolation (STI).
FIG. 7 is a perspective view showing an example of a substrate polishing apparatus used for CMP (hereafter referred to as a CMP apparatus). As shown in FIG. 7, the CMP apparatus performs polishing by pressing a polishing surface of a substrate 3 to be polished held by a disk-shape carrier 1 onto a polishing cloth (polishing pad) 5 mounted on a disk-shape polishing platen 6 (hereafter referred to as a platen 6) at a specified pressure. At this time, the platen 6 is rotating in a specified direction centering a platen shaft 7 which supports the platen 6 at its center, and the carrier 1 is rotating in a specified direction centering a carrier shaft 8 which supports the carrier 1 at its center. The polishing pad 5 is made of closed-cell type polyurethane resin or non-woven fabric for example, and a polishing agent 11 (hereafter referred to as a slurry 11) having colloidal silica or fumed silica as its main ingredient is supplied onto the polishing pad 5 from a polishing agent supply unit 10. By this, the polishing surface of the substrate 3 is polished by the mechanical polishing effect due to friction with the polishing pad 5 and the chemical polishing effect by the slurry 11 so that the unevenness of the polishing surface of the substrate 3 is removed.
Ordinarily, the CMP apparatus has multiple carriers for improving the throughput of the polishing process. The CMP apparatus in FIG. 7 is provided with two pieces of carrier and can simultaneously polish the substrate 3 held by the carrier 1 and a substrate 4 held by the carrier 2 on one polishing pad 5 (hereafter called two-piece polishing).
FIG. 8 is a flow chart showing lot processing with a CMP apparatus which simultaneously polishes multiple pieces (two pieces in the example of FIG. 7) of substrates as one batch. Here, the lot is a process unit consisting of multiple pieces of substrates, and the number of substrates belonging to one lot is greater than the number of substrates processed in one batch.
As shown in FIG. 8, in lot processing, first the number of substrates processed in the same batch are selected from a substrate group constituting of a lot, and are polished with the CMP apparatus (S1→S2 in FIG. 8). When polishing is complete, if an unpolished substrate still remains in the same lot, polishing of the unpolished substrate is continued (S3 Yes in FIG. 8).
At this time, if the number of the unpolished substrates is equal to or greater than the number of substrates in one batch (two pieces here), in the same way as in the previous batch, the same number of substrates as the number of carriers are selected from unpolished substrates in the lot, and polishing is performed using all of the carriers (S4 Yes→S1→S2 in FIG. 8). However, if the number of the unpolished substrates is a fraction of the number of substrates in a batch, either of the following processing is conventionally performed (S4 No in FIG. 8).
The first method is a method wherein a piece of a dummy substrate is added to the lot to create an even number of pieces, and polishing is performed using all of the carriers under the same polishing conditions as that used in polishing the other batches (S5 Yes in FIG. 8).
The second method is a method wherein only the fractional number of substrates is mounted on the carrier, and polishing is performed only with some of the carriers (S5 No→S6 in FIG. 8). In this case, polishing cannot be performed under the same conditions as when polishing other batches, because there is a difference between the polishing rate of the substrate 3 when polishing is performed by mounting the substrate 3 only on the carrier 1 and the polishing rate of the substrate 3 when polishing is performed by mounting the substrates on the carrier 1 and the carrier 2, respectively in FIG. 7, for example. Also, the polishing rate is known to vary due to a polishing time, a polishing pressure when the carrier 1 presses the substrate onto the polishing pad 5, a relative velocity of polishing between the carrier 1 and the polishing pad 5, and a flow rate of the slurry 11, etc. Therefore, polishing is ordinarily performed by setting other conditions to be the same other than the polishing time and varying the polishing time only so that the same amount of polishing can be achieved.
When polishing is complete, if there is no unpolished substrate in the same lot, the lot processing ends (S3 No in FIG. 8).
The polishing time for the CMP polishing of an insulating film formed on a substrate from its initial film thickness to a target film thickness is obtained as follows. In CMP polishing, if the insulating film is formed on a substrate on which a pattern such as wiring is formed and unevenness exists, the polishing rate varies due to the density (sparse or dense) of the unevenness. Therefore, first the polishing time is obtained for a film formed on a substrate without unevenness (hereafter referred to as a flat film), and the polishing time for obtaining a desired amount of polishing can be calculated by using a polishing time multiplying a factor according to the density of unevenness to the polishing time for the flat film.
In general, in a CMP apparatus provided with n carriers, polishing time Tn when polishing with a target polishing amount V is performed on n pieces of substrate in a batch can be calculated using polishing rates R1˜Rn on 1st carrier ˜nth carrier when polishing is performed by mounting a substrate having a flat film on each of 1st carrier ˜nth carrier by Eq. (1) shown below.
                              T          n                =                  f          (                      V            ,                                                            ∑                  n                                ⁢                                                                  ⁢                                  R                  i                                            n                                )                                    (        1        )            
Consequently, the polishing time T2 when polishing with a target polishing amount V by the CMP apparatus in FIG. 7 which performs polishing of two pieces of substrate in one batch can be calculated using the polishing rate R1 for a flat film on the substrate 3 held by the carrier 1 and polishing rate R2 for a flat film on the substrate 4 held by the carrier 2 by Eq. (2) shown below.
                              T          2                =                  f          ⁡                      (                          V              ,                                                                    R                    1                                    +                                      R                    2                                                  2                                      )                                              (        2        )            
Therefore, in case that polishing is performed using all of the carriers, polishing for all substrates belonging to the same lot is performed based on the polishing time T2 calculated from the above Eq. (2).
In case that polishing is performed for a fractional number of substrates using only some of the carriers, the polishing time is calculated (described in Japanese Unexamined Patent Application 2003-249467 for example) based on the polishing rate when polishing is performed in a state wherein a substrate having a flat film is mounted only on the carriers on which the fractional number of substrates are mounted (the carrier 1 in FIG. 7 for example).